Many industrial laundries are located in or near major towns and cities. By their nature they use and discharge substantial quantities of water. Most laundries depend on municipal water treatment plants to treat their effluent, often with limited or no pretreatment by the laundry.
Permissible levels of pollutants, such as oil and heavy metals, have grown increasingly low in recent years making it extremely difficult for many industrial laundries to comply with discharge permits.
Shop towels and mops generate the highest percentage of the oil and heavy metal pollutants that cannot be passed on to a muncipal sewage treatment plant. While the shop towels and mops typically comprise only 20% of the goods processed by the laundry, they may contribute more than 80% of the hydrocarbons and heavy metals in the laundry effluent water. Until now, a satisfactory resolution to this problem has not been found. Some laundries have been forced to install elaborate wastewater treatment facilities at great expense only to find that the cost of operation is prohibitive.
A few years ago a system was developed for cleaning shop towels which was known in the trade as the "Dual Phase System". In this process, an excess of organic solvent (Stoddard Solvent) was used in a first step as a dry cleaning step for removal of grease and oil. The excess solvent then was removed for recycle of the solvent. The towels were then washed in a conventional fashion and the wash water was sufficiently low in solvent that it could be dumped to the sewer for municipal sewage treatment. However, sufficient solvent was retained by the shop towels that touch-up dying of the towels in the water wash steps was difficult, if not impossible. This Dual Phase System resulted in satisfactory cleaning performance and removal of oil from the wastewater. However, the level of solvent carried by the solvent-treated towels going to a drying step was prohibitively high. Organic vapor emissions were unacceptable, resulting in a need for a special dryer recovery system designed to recover the solvent. This was deemed too expensive, and commercially, the process was abandoned.
As set forth in U.S. Pat. No. 3,473,175, it is well known in the dry cleaning industry to initially pre-soak textiles in a bath of pure organic solvent and only thereafter allow water to enter the cleaning apparatus for cleaning the fabric in an emulsion of water dispersed in an organic solvent, such as perchloroethylene. As set forth above, one of the major problems with this method of cleaning heavily soiled industrial laundry is in the separation of the cleaning solvent from the water since a high percentage of the cleaning solvent is left in the fabric. Consequently, careful and expensive stripping apparatus must be used to insure that the solvent stripped from the fabric does not enter the atmosphere in order to comply with EPA requirements and regulations.
One of the most serious drawbacks of prior art methods and apparatus for cleaning heavily soiled industrial laundry is that a large excess of cleaning solvent is used beyond that which is necessary to soak the soiled laundry and, in addition, substantial quantities of water are mixed with this cleaning solvent in order to provide the number of wash cycles necessary to achieve the desired cleaning effect, resulting in serious problems in separating the solvent from the water. In accordance with the present invention, the soils from heavily soiled industrial laundry are removed and concentrated in small amounts of water and small amounts of solvent so that the separation procedure is unexpectedly more efficient for recycle of solvent to the cleaning operation than was possible in extant methods and apparatus while allowing water from the water wash cycles to be dumped to the sewer for municipal sewage treatment.